1. Field of the Invention
The present invention relates to an electronic timepiece with an internal antenna such as a radio-controlled timepiece that receives external wireless information including time information and adjusts the displayed time accordingly.
2. Description of the Related Art
Electronic timepieces with an internal antenna, such as radio-controlled watches that adjust the displayed time based on time information received from an external source, are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. 2003-161788.
In such an electronic timepiece the internal antenna is housed in a first watch case made of plastic or other non-conductive material. The first watch case is covered with a metal second watch case that has a notch formed in a portion thereof. The opening of the antenna loop is rendered opposite this notch so that radio signals can be received by the antenna without being blocked by the metal case.
While watches of this type can thus have a metal exterior and accordingly a high quality appearance, two different cases made of different materials are required, and a notch must be formed in the conductive case. Manufacturing is thus more difficult, and the production cost is therefore higher.
There are also electronic timepieces with an internal antenna in which the watch case is plastic. However, such watches, compared with watches having a metal case, have a less attractive design and a low quality appearance.
Furthermore, while a common rod antenna can be rendered inside a metal watch case as taught in the cited Japanese Pub. 2003-161788, this results in a rather large watch case. More specifically, if the ends of the antenna core are close to the inside surface of the case, radio signals are attenuated by the metal case and the reception sensitivity of the antenna thus drops. The antenna core ends must therefore be separated a certain distance from the inside surface of the case. In addition, the antenna must be of a certain minimum length determined by the type of radio signals received. With these constraints, in order to render an antenna of a specific length inside the watch case with the antenna ends separated a certain distance from the inside surface of the case, a larger watch case is required. This is undesirable.
This problem is not limited to radio-controlled timepieces, and is common to all electronic timepieces with an internal antenna for radio communication.